Construction Manual of Merlin spectrometer The first generation of our Merlin Spectrometer is based on the ramanpi Spectrometer. The Project was developed open source with a detailed construction documentation. In the link below you will find some details. https://hackaday.io/project/1279-ramanpi-raman-spectrometer/log/9583-how-to-build-aspectrometer In the working progress we optimized Merlin for our challenges, added some features for calibration, sample handling and other adjustments. In the following part list you will find everything you need for your very own Merlin spectrometer. Furthermore you need access to a 3D-printer to print your spectrometer casing and other components. 1
Step by step preparations and assembly Attention! The diffraction grating and the mirrors should be handled carfully. We recommend disposable gloves and hexagon socket screws to prevent scratches and fingerprints. Be careful when preparing the gap. When working with the shaving blades and the magnet you can easily cut yourself. First step - download and get started with the 3D-prints Download every print-file on our website for your own spectrometer and print Merlins spectrometer casing. After printing remove all unnecessary support structures and free every srcew hole. Before all components are installed, it is recommended to put all screws into the housing. Furthermore you need to print the two mirror holders, the diffraction grating mount, and the frame for the CCD modul. Second Step - fixing optical components to the corresponding holders Fix the optical components to the corresponding sockets with double-sided adhesive tape. The fixation is secured with a little glue. The diffraction grating frame is secured in the lower area between the frame and the case with a round thin latex strip. The rubber ring is removed from a disposable glove and ensures the security and rotation for later calibration. Third Step - Prepare slit or small hole For a narrow gap, two razor blades (7mm * 15mm) are cut out of a razor blade with scissors covering the hole of the magnet to create a fine gap with the desired gap width. The gap is fixed with scotch film without sticking over the gap. For a small square hole, work is done equivalently with four cut razor blades. Optimize the gap width for your requirements and note that as the gap size decreases, the spectral resolution increases and the intensity decreases. 2
Fourth step - CCD modul Complete the TCD1304 Linear CCD module following the instructions of Esben Rossel. His detailed instructions can be found in the following link: https://hackaday.io/tvaettbjoern We used a Otter T1304 PCB board, which has the same port constellation as Esben Rossel s second SMD-Version. For the PCB board you will need resistors, capacitors, ports; IC, Transistors with following specifications (table 1).To make the depths of the CCD sensor adjustable, we inserted two layers of the socket strips. We recommend to provide the six jumper cables with markings for the connections. Table1 specifications fort he CCD modul R1; R2 150Ω SMD 1206 R3 2,2 kω SMD 1206 C1; C3 0,1 μf SMD 1206 C2 10 μf SMD 1206 T1 2SA1015-Y IC1 TC74HC04 SMD 1206 CCD TCD1304 Socket strips1 (ST1) 4x 11 Female headers BLY 1 Socket strips2 (ST2) 2x 5 Female headers BLY 1 PCB board The Otter TCD1304 board 6 jumper cables Figure1: Interior view of the PCB board within Merlin on which the ccd sensor is placed on a two-layer socket strips1 (ST1). In the link below you can find more details about the PCB board: http://dirtypcbs.com/store/details/863/the-otter-tcd1304-board 3
Table2 How to connect the CCD modul with the nucleo 1 fm connects to PB0 (A3) 2 SH connects to PA1 (A1) 3 ICG connects to PA0 (A0) 4 OUTPUT (OS) connects to PC0 (A5) 5 +5V connects to +5V 6 GND connects to GND Figure 2: The corresponding external view of the PCB board within Merlin to which the IC1, C1, C2, C3, R1, R2, R3, T1 and the socket strips2 (ST2) are soldered. Fifth step - final assembly Upon completion of all preparations, all items can now be located at their intended location in the lower part of the spectrometer housing, as shown in figure 3. Figure 3: lower half of the Merlin spectrometer with built-in components. 4
Sixth step - calibration For coarse calibration, a laser with a defined wavelength is recommended. We used a laser with a wavelength of 650 nm and a power of 0.4 mw, which represents only a low risk for the eyesight. When calibrating with the slit and the above-mentioned laser, it is urgent for a good spectral resolution that the distance from the slit opening to the first small spherical mirror correspond exactly to the focal length of 8 cm so that the reflected light beam is collimated to the diffraction gratingthe distance between the large concave mirror and CCD sensor must also be adjusted with great care to the focal length of 10 cm. After appropriate adjustment of the distances and angles, a vertical narrow red stripe is imaged on the CCD sensor, which is located relatively far to the right of the sensor. A mercury lamp is excellently suited for calibration with its wide discrete light spectrum and provides information on which wavelength range is imaged on the CCD sensor. Each light source with known and constant light spectrum in the visible range is suitable for calibration of the Merlin spectrometer. When evaluating the measured values, it should be noted that the spectral response of the CCD sensor is not constant and drops significantly as of a wavelength of 700 nm. You can find more details in the link below: https://www.coptonix.com/html/laith_i_ccd.html Figure 4: Completed Merlin spectrometer with outer case, nucleo, Raspberry Pi and LCD display. 5
Figure 5: Ready-to-use Merlin spectrometer after fine calibration. After careful alignment and verification of the spectral resolution. Can the measurement signals be evaluated via a laptop or the Raspberry PI. Note, intensity peaks are inverted by the CCD sensor as valleys. Have fun and success with your Merlin spectrometer! 6